Accepted to Yale, he deferred to join the Navy (to whom he had to lie about his age, he was 17, too young to enlist) and served in combat as a TBM Avenger pilot. He was hit by enemy fire, and shot down, but managed fly on and to hit the target even after his airplane had been hit. He was awarded the Distinguished Flying Cross. After the war ended, at Yale, he played baseball, and had a lifelong affinity for both the sport of baseball and naval aviation.
His hand-written letter to his Presidential successor is the epitome of class, and has gone viral. Google it. Read it. You'll understand him better.
A great man and humble servant. When I retired from the Navy a few years ago, I asked his staff for a Presidential Certificate, as he was Commander in Chief when I flew my first combat mission, and while I still need to frame it and hang it up in my study, that one bit of paper means a great deal to me.
A friend sent me this photo this afternoon, from June, 1948, of a young Yale first baseman meeting the great Babe Ruth.